1. Field of the Invention
The present invention relates to a method and apparatus for aggregating a plurality of carriers in a wireless access system and using the aggregated carriers, and more particularly to a method and apparatus for providing information about a carrier structure formed by aggregating several carriers.
2. Discussion of the Related Art
A brief description of carriers will be given hereinbelow.
The amplitude, frequency, and/or phase of a sine wave or a periodic pulse wave may be modulated to include information. The sine wave or pulse wave serving to convey information is called a carrier.
Methods for modulating a carrier include single-carrier modulation (SCM) and multi-carrier modulation (MCM). SCM performs modulation such that all information is carried on a single carrier.
MCM divides an entire channel bandwidth of one carrier into subchannels having multiple narrow bandwidths and transmits multiple narrowband subcarriers through respective subchannels.
When using MCM, each subchannel may approximate to a flat channel due to a narrow bandwidth. A user may compensate for distortion of a channel using a simple equalizer. MCM may be implemented at a high speed using Fast Fourier Transform (FFT). Namely, MCM is favored over SCM during high-rate data transmission.
In the embodiments of the present invention, a multi-carrier system supporting broadband by aggregating one or more carriers is proposed. Specifically, the multi-carrier system, which will be described hereafter, uses carriers by aggregating one or more carriers, unlike the afore-mentioned MCM which uses carriers by segregating one carrier.
To efficiently use multiple bands or multiple carriers, a technique in which one medium access control (MAC) entity manages multiple carriers (e.g., multiple frequency carriers) has been proposed.
FIGS. 1(a) and 1(b) illustrate methods for transmitting and receiving signals based on a multi-band radio frequency (RF) scheme.
In FIGS. 1(a) and 1(b), one MAC layer in each of a transmitting end and a receiving end may manage multiple carriers to efficiently use the multiple carriers. To effectively transmit and receive the multiple carriers, it is assumed that both the transmitting end and the receiving end can transmit and receive the multiple carriers. Since frequency carriers managed by one MAC layer do not need to be contiguous, the above method enables flexible resource management. More specifically, the frequency carriers may have contiguous aggregation or non-contiguous aggregation.
In FIGS. 1(a) and 1(b), physical layers (PHY 0, PHY 1, . . . , PHY n−2, and PHYn−1) represent multiple bands and each of the bands may have a frequency allocation (FA) band size allocated for a specific service according to a predetermined frequency policy. For example, PHY 0 (RF carrier 0) may have a frequency band size allocated for a general FM radio broadcast and PHY 1 (RF carrier 1) may have a frequency band size allocated for cellular phone communication.
Although each frequency band may have a different FA size depending on the characteristics thereof, it is assumed in the following description that each frequency carrier (FC) has a size of A MHz for convenience of explanation. Each frequency allocation (FA) band may be represented by a carrier frequency that enables a baseband signal to be used in each frequency band. Thus, in the following description, each FA will be referred to as a “carrier frequency band” or will simply be referred to as a “carrier” representing each carrier frequency band unless such use causes confusion. As in the recent 3rd generation partnership project (3GPP) long term evolution-advanced (LTE-A), the carrier may also be referred to as a “component carrier” to discriminate it from a subcarrier used in the multi-carrier system.
As such, the “multi-band” scheme may also be referred to as a “multi-carrier” scheme or a “carrier aggregation” scheme.
In order to transmit a signal through multiple bands as shown in FIG. 1(a) as well as to receive a signal through multiple bands as shown in FIG. 1(b), it is necessary for a transceiver to include a Radio Frequency (RF) module that transmits and receives signals through multiple bands. In FIG. 1, a method for constructing the MAC layer “MAC” is decided by a base station (BS) irrespective of downlink (DL) and uplink (UL).
In brief, FIG. 1 shows signal transmission/reception technology for enabling one MAC entity (simply referred to as a MAC) to manage/operate a plurality of RF carriers. In addition, RF carriers managed by one MAC need not be contiguous to one another. Therefore, the above-mentioned signal transmission/reception technology of the present invention is more flexible in terms of resource management. However, according to user requirements or channel environment, a MAC entity for each carrier can manage/operate individual carriers as shown in FIG. 1.
FIG. 2 exemplarily shows a frequency allocation method for use in a carrier aggregation system.
In FIG. 2, frequency allocation bands (FA 0 to FA 7) may be managed by RFs (RF 0 to RF 7). In FIG. 2, it is assumed that FA 0, FA 2, FA 3, FA 6 and FA 7 have already been allocated to a specific conventional communication service. In the meantime, available RFs (RF 1(FA 1), RF 4(FA 4), and RF 5(FA 5)) can be effectively managed by one MAC (MAC #5). In this case, RF carriers constructing one MAC may not be contiguous to one another as described above, such that it is possible to more effectively manage frequency resources.
From the viewpoint of downlink, it is possible to use the following exemplary base station (BS)/mobile station (MS) scenario in association with the multi-band supporting scheme or the carrier integration scheme.
FIG. 3 shows an exemplary scenario for communicating between one BS and several MSs for use in a multi-band scheme.
In FIG. 3, it is assumed that MS 0 (or UE 0), MS 1 (or UE 1) and MS 2 (or UE 2) are multiplexed. BS 0 (or Node-B 0) may transmit a signal through a frequency band managed by carriers RF 0 and RF 1. In addition, MS 0 has throughput for receiving only RF 0, and MS 1 can receive both RF 0 and RF 1. In this case, MS 2 can receive signals of only RF 0 and RF 1 because the BS transmits only RF 0 and RF 1.
A general wireless communication system transmits data using one bandwidth (i.e., one carrier). In order to increase transmission capacity of RF data, a system bandwidth for use in a second generation mobile communication system has been extended to 200 KHz˜1.25 MHz, and a system bandwidth for use in a third generation mobile communication system has been extended to 5 MHz˜10 MHz.
In addition, the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) system or the Institute of Electrical and Electronics Engineers (IEEE) 802.16m system has attempted to extend system bandwidth up to 20 MHz.
In order to increase transmission (Tx) capacity of RF data, a method for increasing bandwidth is needed. However, it is necessary to support a large bandwidth even when a currently requested service is low in level, such that a large amount of power may be unavoidably consumed. In addition, the current system cannot be reused to support such requirements. In order to solve the above-mentioned problems, a multicarrier transmission method for simultaneously transmitting/receiving a plurality of bandwidths is an area of intense research. Recently, grouping one or more multicarriers is referred to as carrier aggregation.
However, a multiband-based communication scheme for use in a current mobile communication technology has been conceptually defined. If necessary, the multiband-based communication scheme may require further assignment of only a Frequency Assignment (FA).
Therefore, a multiplexing method and a multiplexed carrier aggregation structure to implement more efficient and higher-performance processing, and methods for transmitting/receiving information of a carrier aggregation structure need to be more specifically defined.